Jellyfish: Scyphozoa

Jellyfish have one or both of two body forms: bottom-dwelling polyp and freely swimming medusa. The medusa (mi-DOO-suh) is the jelly-like, usually bell- or umbrella-shaped, usually tentacled form. The polyp (PAH-luhp) consists of a tubular sac with a mouth and tentacles on top. Polyps are less than one-eighth inch (4 millimeters) long. Medusae (mi-DOO-see, the plural of medusa) can be as large as 80 inches (2 meters) in diameter. Near the edge of the bell most jellyfish have tentacles used for feeding. The tentacles have millions of stingers that inject toxin into or entangle their prey. Some jellyfish have hundreds of these tentacles. Rather than tentacles, some jellyfish have mouth arms on the underside of the bell. These arms also have stingers for feeding. Other jellyfish have one thick tentacle on the upper surface of the bell. Some jellyfish have a stalk that they attach to seaweed or sea grasses. Stalked jellyfish have eight arms, each bearing a cluster of as many as one hundred short, clubbed tentacles.